The prior electric saw, particularly a jig saw, is mainly used to cut wood, steel plate, plastic and so on by a motor to reciprocate a saw blade. In order to align the saw blade with a cutting line on a workpiece, the operator must typically bring the blade into contact with the workpiece to determine if the saw is properly aligned with the cutting line. As is familiar to those skilled in the art, such a jig saw has some disadvantages. First, the operator is required to concentrate his observation exactly ahead of the cutting blade as the blade is pushed along the prescribed and prepared target line, it has to repeat this procedure several times in order to achieve proper alignment for precision, and this will result in waste of time and material. Also, the target line exactly ahead of the cutting blade may be covered by chip dust and influence the alignment of saw blade with the cutting line.